AR_final file_2018-19

Observational Cosmology Cosmology from cosmic shear power spectra with Subaru Hyper Suprime- Cam first-year data The gravitational lensing effect in Einstein’s gen- eral theory of relativity causes the shapes of back- ground galaxies to get distorted due to the gravita- tional field of the intervening large scale structure. By measuring the exquisite images of about 9 mil- lion galaxies taken with the Subaru telescope us- ing the Hyper Suprime-Cam (HSC) camera, which measured the weak lensing effect. The cosmic weak lensing shear power spectra were measured using the data from the Subaru HSC survey first-year shear catalogue covering 137 sq deg of the sky. A careful accounting of various uncertainties in the analysis including the intrinsic alignment of galax- ies, scatters and biases in photometric redshifts, residual uncertainties in the shear measurement, and modelling of the matter power spectrum, al- lows to infer the amplitude of density fluctuations in the Universe. For a flat lambda-dominated cold dark matter model, Surhud More and collaborators were able to constrain the amplitude of density fluctuations with an accuracy of 3.5 percent. In comparison with Planck cosmic microwave background con- straints, these results prefer slightly lower values of these amplitude of density fluctuations, although metrics such as the Bayesian evidence ratio test do not show significant evidence for discordance between these results. The ongoing full HSC sur- vey data will contain several times more area, and will lead to significantly improved cosmological con- straints. Assembly bias of cool core clusters traced by H α nebulae Do galaxy clusters with cool-core (CC) live in dif- ferent environments compared to those with a non- cool-core (NCC)? By making novel use of the H α emission lines in the central galaxies of optically se- lected galaxy clusters as proxies to construct large (1,000’s) samples of CC and NCC clusters, the rela- tive assembly bias of these galaxy clusters was mea- sured using both clustering and weak lensing. The measurements of cross-correlation of these galaxy clusters with an external galaxy redshift catalog from the Sloan Digital Sky Survey III, the LOWZ sample, allowed for an increase in the statistical significance of the results. These cross-correlations can be used to constrain assembly bias up to a sta- tistical uncertainty of 6 percent. Given the H α cri- teria for CC and NCC, the study involving Surhud More and collaborators, found no significant dif- ferences in the clustering amplitude. Interpreting this difference as the absence of halo assembly bias, these results rule out the possibility of having differ- ent large-scale (tens of Mpc) environments as the source of diversity observed in cluster cores. Com- bined with recent observations of the overall mild evolution of CC and NCC properties, such as cen- tral density and CC fraction, the results suggest that either the cooling properties of the cluster core are determined early on solely by the local ( ≥ 200 kpc) gas properties at formation or that local merg- ing leads to stochastic CC relaxation and disrup- tion in a periodic way, preserving the average pop- ulation properties over time. Studying the small- scale clustering in clusters at high redshift would help shed light on the exact scenario. Fourier Power Function Shapelets (FPFS) shear estimator: Perfor- mance on image simulations Surhud More and collaborators have reinter- preted the shear estimator used to measure shapes of galaxies for weak gravitational lensing developed by Zhang and Komatsu within the framework of shapelets, and have proposed the Fourier Power Function Shapelets (FPFS) shear estimator. Four shapelet modes are calculated from the power func- tion of every galaxy’s Fourier transform after decon- volving the point-spread function (PSF) in Fourier space. They proposed a normalization scheme to construct dimensionless ellipticity and its corre- sponding shear responsivity using these shapelet modes. Shear is measured in a conventional way by averaging the ellipticities and responsivities over a ( 65 )